The structural and functional alterations in initiation factors induced by poliovirus infection will be studied. Monoclonal antibodies will be prepared against discrete polypeptide components of eIF3 and cap binding proteins (CBP) for use in defining their structures, interactions and activities in infected and uninfected cells. In particular, a newly-discovered virus-induced cleavage of an eIF3-related polypeptide, M(r) 210 kilodaltons (p210), will be studied to determine the relationship of this polypeptide to eIF3 and/or CBP. The mediator of p210 cleavage will also be determined. Experimental approaches include immunoblot analysis of cell lysates and partially purified factors from infected and uninfected cells,,and correlation of the presence of individual polypeptides with defined In Vitro activities. Also antibody-inhibition studies of crude and purified cell-free translation systems will be performed to determine the polypeptide requirements for translation of capped and uncapped messenger RNA's. These studies will aid in precisely defining the polypeptide composition of initiation factors eIF3 and CBP, and in determining their roles in translation. They address the more general question regarding the mechanism of messenger RNA discrimination in protein synthesis.